1. Field of the Invention
The present invention relates to a method for generating a mesh of an object for three-dimensional analysis used in the finite element method or the finite volume method.
2. Description of the Related Art
An automatic mesh-generating method in which a mesh of a three-dimensional object is automatically generated by decomposing the object into small, hexahedral elements is known in the art. In this method, the shape of the object whose mesh can be generated is limited. An automatic mesh-generating method which can be applied to an object having any shape, for decomposing the object into small, tetrahedral elements is also known in the art. This method is used in commercial tools such as IDEAS, Solid Designer, and Patran. However, this method of decomposing an object into tetrahedral elements has a disadvantage in that the precision of the analysis decreases if the object has a high aspect ratio, in other words, if the object has a distorted shape.
In particular, when the object has a high aspect ratio on the surface thereof, the precision of the analysis decreases considerably and it may even be impossible to perform the calculation. In addition, there is also a disadvantage in that the decomposition into tetrahedral elements requires a longer calculation time than the decomposition into hexahedral elements since larger numbers of nodes and elements are generated.
Accordingly, in mesh-generating programs for fluid analysis such as STAR-CD, Pro-am and CFX-Build, a mesh of an object is generated by creating triangles on the surface of the object, projecting the triangles into the object for a small distance to generate pentahedral elements called prisms or pentas, and decomposing a three-dimensional region remaining in the object into tetrahedral elements.
In addition, another automatic mesh-generating method for a three-dimensional object is disclosed in Japanese Patent No. 2,941,653. According to this method, a portion of the object is decomposed into hexahedral elements, and the remaining portion of the object is decomposed into tetrahedral elements.
On the other hand, in a simulation of an injection molding process, the object to be analyzed is thin-walled. Since this thin-walled part has a large temperature variation across the thickness and even more so at thin portions thereof, these thin portions are preferably decomposed into a plurality of layers in the thickness direction. In addition, since molten regions of the thin-walled part vary particularly along the surfaces thereof, mesh elements in the same layer preferably have a uniform size.